Suppression of vertically polarized radiation from an omnidirectional range antenna system



Aug. 21, 19 6 J. P. SHANKLIN 2,760,192

SUPPRESSION OF VERTICALLY POLARIZED RADIATION FROM AN OMNI-DIREICTIONAL RANGE ANTENNA SYSTEM Filed NOV. 16, 1954 4 Sheets-Sheet l INVEN TOR.

JOHN P! SHANKL. IN

ATTORNEy g- 1955 J. P. SHANKLIN 2,760,192

SUPPRESSION OF VERTICAL-LY POLARIZED RADIATION FROM AN OMNI-DIRECTIONAL RANGE ANTENNA SYSTEM Filed NOV. 16, 1954 4 Sheets-Sheet 2 INVENTOR. WG- j Jon/v P. SHANKLIN ATToRNEy g- 1956 J. P. SHANKLIN 2,760,192

SUPPRESSION OF VERTICALLY POLARIZED RADIATION FRCM AN OMNI-DIRECTIONAL RANGE ANTENNA SYSTEM Filed NOV. 16, 1954 4 Sheets-Sheet 3 42 & r L

f Y T J J6 B S36 JG ZF1Ia; 6

INVENTOR. HG Z JOHN P. SHANKLIN ATToRIvEy 1956 J. P. SHANKLIN 2,760,192

SUPPRESSION OF VERTICALLY POLARIZED RADIATION FROM AN OMNI-DIRECTIONAL RANGE ANTENNA SYSTEM Filed NOV. 16, 1954 4 Sheets-Sheet 4 7b PowER JouRcE Irvpu-r IN V EN TOR.

JoHrv-P. SHANKLIN ATToRrvEy United States Patent SUPPRESSION 0F VERTICALLY POLARIZED RADIATION FROM AN ONINIDIRECTIONAL RANGE ANTENNA SYSTEM John P. Shanklin, Cedar Rapids, Iowa, assignor to Collins Radio Company, Cedar Rapids, Iowa, a corporation of Iowa Application November 16, 1954, Serial No. 469,185

9 Claims. (Cl. 343-727) This invention relates generally to navigational antenna systems and particularly to means for suppressing undesired vertically polarized directional radiation from a horizontally polarized navigational antenna system.

The invention concerns an antenna system used in an omni-directional radio beacon, sometimes known as omnirange. The Civil Aeronautics Administration requires that omni-range beacons provide horizontally polarized radiation. Administration regulations further require that the radiation have a cardioid-type pattern in the horizontal plane and that it rotate at thirty revolutions per second. The cardioid-type pattern is shown as item 10 in Figure l and results from the instantaneous summation in the horizontal plane of an omni-directional radiation pattern 11 and a figure-eight radiation pattern 12. Patterns 11 and 12 are horizontally polarized to provide horizontally polarized pattern 10.

An aircraft, flying within 100 miles of the omni-range station and carrying an antenna designed to receive horizontally polarized radiation, receives signals from the omni-range antenna and carries a computer that determines the direction of the aircraft with respect to the transmitting antenna. The computation, which is accomplished electronically, compares a frequency modulated signal, that is uniform in all directions and is carried by omni-directional radiation pattern 11, with an amplitude modulated signal, caused by the rotating cardioidtype pattern.

Unfortunately, no omni-directional range transmitting antenna is known which transmits a pure horizontally polarized signal without any vertically polarized components. Although small, these vertically polarized signals are unwittingly picked up by an aircraft antenna, and they introduce error in the navigation computer of the aircraft to provide the pilot with navigation information that is correspondingly in error. No aircraft antenna is known which will always totally discriminate between horizontally and vertically polarized signals. Even antennas, which would provide such discrimination if isolated, have their characteristics modified by the curved metallic surfaces of the aircraft so that they are to some degree sensitive to vertically polarized signals. Furthermore, if a perfect antenna were known, it still would receive vertically polarized signals when the aircraft banks to make a turn.

This invention provides an omni-directional range transmitting antenna system wherein the vertically polarized components cancel each other at those vertical angles that are used by aircraft while distant from the beacon. The vertically polarized components are suppressed by the invention over a large vertical angle that is uniform in all horizontal directions. Due to the curvature of the earth, an aircraft approaching the transmitter will initially be below the horizon and will pass into the angle of suppressed vertical components as it approaches the station. At all places except where ahnost above the beacon, the aircraft will be flying where there is almost no vertically polarized signal. The error in position, caused by the vertically polarized components, is significant only while the aircraft is distant from the omni-range beacon; and hence, the invention suppresses the error causing radiation where it would be harmful.

It is therefore an object of this invention to suppress over a large vertical angle and uniformly in all horizontal directions the vertically polarized components from an omni-directional range antenna system, comprising a rotating dipole antenna within a slotted cylinder antenna.

It is another object of this invention to teach how a slotted cylinder antenna, containing a dipole antenna and located in outer space, may be formed to provide cancellation of certain vertically polarized radiation components.

It is still another object of this invention to teach how a slotted cylinder antenna, containing a dipole antenna and located adjacent to a ground plane, may be formed to provide cancellation of certain vertically polarized radiation components.

It is a further object of this invention to provide a ground-plane with an adjustable outer diameter in combination with a slotted cylinder antenna containing a dipole antenna, wherein the ground-plane is adjustable to assist in the substantially complete cancellation of certain vertically polarized radiation components.

The invention includes a slotted cylinder antenna that may have a diameter as small as 0.1 of a wavelength at the radiated frequency and is mounted in an upright manner above the center of a circular ground plane. The cylindrical antenna is formed with a plurality of slots that are positioned uniformly about the cylinder with their longest dimension located axially of the cylinder.

A rotating dipole is supported within the cylindrical antenna and is rotated in a horizontal plane that intersects the midportions of the slots. The dipole induces certain vertical currents in the cylindrical antenna that cause the undesired vertically polarized radiation.

The cylindrical antenna is formed with particular attention given the axial dimensions of its unslotted portions located above and below the slots. These dimensions control the suppression of vertically polarized components caused by the dipole induced vertical currents. If the antenna system were located in free space, the upper and lower cylindrical portions would be formed with equal axial dimensions to suppress the vertically polarized components in the equatorial plane of the cylin der. However, when the antenna system is located adjacent to a ground plane, as is ordinarily the case, the upper axial dimension of the cylinder must be slightly greater than the lower axial dimension to provide proper cancellation of the vertical components.

The diameter of the ground-plane is important; and it has been found that a ground-plane with a radius that is calculated as explained below particularly assists in the suppression of the vertically polarized components. A plurality of radially extending rods are provided by this invention about the periphery of the ground-plane so that it may be adjusted to provide complete suppression of the most undesired vertical components.

Generally, in prior slotted cylinder antennas, the cylinders were also used as waveguides or cavity resonators to convey energy to the slots; and sometimes, dipole shapzed probes were used to inject energy into the waveguide or cavity. The present invention does not use the cylinder as a waveguide transmission line or cavity resonator but uses a feed system which permits the slotted cylindrical antenna to have a diameter as small as 0.1 of a wavelength which is substantially smaller than the minimum diameter of 0.58 wavelength for a cylindrical wave guide or hollow cavity resonator.

The slotted cylinder feed system in the invention uses a system of individual conductors which connect together at one of their ends. One end of an unbalanced input transmission line connects on one side to this common connection and on the other side to a metallic member connected to the cylindrical antenna. Each feed conductor passes insulatingly along the internal surface of the cylinder to a different slot, which it passes over in a transverse manner to connect to the midpoint of the opposite side of the slot. The radio-frequency energy fed to the cylindrical antenna may be modulated to provide side-band energy that is uniform in all horizontal directions.

The internal dipole antenna may be rotated by a synchronous motor supported within the cylindrical antenna without disturbing the transmission of energy to the slots. A balanced source of radio-frequency energy may be electrically connected to the dipole by means of a pair of rotary condensers connected serially to the respective sides of the dipole, thereby avoiding any mechanical connection in the transmission of energy to the whirling dipole. Also, balanced inductances may be provided serially in this input line and adjacent to the dipoles so that the length of the dipoles may be reduced considerably less than one-half a wavelength. Hence, the dipole length may be reduced to correspond to a reduction in the diameter of the slotted cylinder to substantially below one-half a Wavelength.

Further objects, features and advantages will be obvious to a person skilled in the art upon further study of this specification and drawings, in which:

Figure 1 illustrates an instantaneous horizontal radiation pattern provided by an omni-directional range antenna system.

Figure 2 shows a vertical pattern of vertically polarized radiation provided by this invention in free space.

Figure 3 is an elevational view of an embodiment of the invention.

Figure 4 is a perspective view of the apparatus shown in Figure 3.

Figure 5 is a detailed view of an adjustable groundplane rod used in the invention.

Figure 6 is an axial sectional view of the omni-directional antenna and its feed system used in the invention.

Figure 7 is a cross-sectional view of the omni-directiona] antenna and its feed system taken along line 77 in Figure 6.

Figure 8 is a cut-away perspective view of the slotted cylinder antenna showing an internally contained dipole antenna and its motor.

Figure 9 is a schematic diagram of the dipole antenna and its associated circuitry.

Figure 10 is a perspective view of the slotted cylinder antenna, showing the paths of induced currents caused by mutual coupling between the antennas.

Now referring to the invention in more detail, Figure 3 shows an elevational view of a chosen embodiment which has a base housing that is shown situated on the surface of the earth 21, but it may also be situated on a vehicle. Base 20 generally houses transmitting equipment (not shown); and a door 22 is provided for accessibility. A circular ground-plane 23 is fastened horizontally across the top of housing 20; and a plurality of equally spaced rods 24 extend radially from the periphery of ground-plane 23. Rods 24 are adjustable radially of ground-plane 23 and may be supported by means of brackets 26, shown in detail in Figure 5. Each bracket 26 is attached near the edge of the ground-plane and receives slideably one of the ends of rods 24 which may be fixed in position by a set-screw 27. The spacing between adjacent rods 24 should not be over one-quarter wavelength at the radiated frequency and may be any amount less than this.

A slotted cylindrical antenna 31 is supported vertically above the center of ground-plane 23 by an outer support 32 of insulating material; and an inner support 33 of metallic material is fastened coaxially at its bottom. to ground-plane 23 and is fastened coaxially at its upper end to an annular cover member 35 (shown in Figure 6) that is fixed across the bottom of antenna 31. A domed top member 34 of metallic material is fastened conductively across the upper end of slotted cylindrical antenna 31.

Slotted antenna 31 is formed with a plurality of slots 36 which may have any number greater than four. The disclosed embodiment has twelve slots 36. Each slot 36 is rectangular in shape, and its long dimension, which may be approximately one-half wavelength at the radiated frequency, is formed axially of the cylinder. The sl-ots have equal lengths, and their upper and lower ends are aligned in respective hypothetical horizontal planes. The vertical midpoints of the slots are located in a horizontal plane, designated as equatorial plane 96, that is spaced in Figure 3 above ground-plane 23 by the dimension H. The unslotted portion 37 of cylinder 31 above slots 36 has an axial dimension, designated as A; and the unslotted portion 38 of cylinder 31 below the slots has an axial dimension designated as B, as shown in Figures 3 and 6. The size of dimensions A and B is important in this invention and will be explained in more detail below.

The structure of the radio frequency feed-system for cylindrical antenna 31 is shown in Figures 6 and 7. The system includes a coaxial input line 41, which passes from the transmitter in housing 20 through an opening in lower cover member 34, to the inner surface of cylinder 31 where it passes upwardly between any pair of adjacent slots 36 to dome 34. Cable 41 is supported at the inner surfaces of cylinder 31 and domed top 34 by brackets 42. The outer conductor 43 of 08.13116 41 connects electrically to dome 34, and its inner conductor 44 extends outwardly and connects to the center of a common connecting member 46 which is supported adjacent to and coaxial of domed top 34.

A plurality of conductors 47, equal in number to slots 36, are located within cylindrical antenna 31. They connect at one end symmetrically about common connecting member 46 and fan outwardly. Each conductor 47 is supported insulatingly from the inner surfaces of domed top 34 and cylindrical antenna 31 and passes downwardly between a different pair of slots 36.

After passing downwardly between its respective slots, each conductor 47 turns in a counterclockwise direction in Figure 7, passes transversely over the rnidportion of its slot 36, and connects at its remaining end to the opposite side of the slot.

The dipole antenna 51 is supported rotatably within cylindrical antenna 31 and is fixed by a cap support 52 to the end of the shaft of a synchronous motor 53, which is supported axially within the cylindrical antenna 31 by symmetrical support 55. An enclosure 54 is fastened to the upper end of motor 53 and has within it apparatus used in conjunction with dipole antenna 51. Dipole 51 rotates in a horizontal plane that intersects the vertical midpoints of slots 36 and rotates about an axis coincident with the axis of cylindrical antenna 31.

Another coaxial tranmission line 56 passes from the transmitter apparatus in housing 20 to cylinder 31 and passes into enclosure 54 to carry radio-frequency energy to the dipole. A power line 57 connects at one end to the power input of motor 53 and connects at its other end to a source of synchronous power, which might be a sixty cycle per second source.

Enclosure 54 is schematically shown in dotted lines in Figure 9, and it shields and supports a balun transformer 58 which is connected on its input side to coaxial cable 56. Balun 58 changes the unbalanced energy received from cable 56 to balanced energy and provides an output impedance which matches the dipole impedance.

A pair of rotary condensers 61 and 62, which are also supported in enclosure 54, have fixed plates 63 and 64 supported by the stator member of motor 53, and rotary plates 66 and 67 supported by the rotor member of motor 53. The fixed plates connect respectively to opposite sides of the output of balun 58. The rotary plates 66 and 67 are fixed to the respective sides of the dipole and, hence, rotate with dipole 51 to provide transmission of radio-frequency energy from fixedly supported balun 58 to rotating dipole 51 without any mechanically rubbing parts.

A pair of inductances 68 and 69 are supported within cap support 52. Accordingly, they rotate with dipole 51, and each is connected serially with one of the respective dipole sides 71 and 72 to enable dipole 51 to have a length substantially less than one-half a wavelength at the radiated frequency in order that it may operate within a slotted cylinder antenna, which has a diameter substantially smaller than one-half of a wavelength.

A single transmitter ordinarily is used to supply energy to both the cylindrical and dipole antennas in which case a phase-adjusting member is generally provided in the transmission line connected to one of the antennas. Also, it is often required that the energy radiated by the cylindrical antenna be modulated; and accordingly, it is then required that some means of modulation be connected to the input of the omi-directional antenna.

The invention acts to control certain types of vertically polarized radiation from the above described omni-range antenna system without in any manner interfering with its horizontally polarized radiation patterns. Cardioidtype pattern in Figure 1 shows the intensity pattern in the horizontal plane of the total radiated carrier-frequency energy that is horizontally polarized. Pattern 10 is the result of the vectorial addition in space of two component radiation patterns, which are a uniform pat tern 11 provided by cylindrical antenna 31 and a figureeight pattern 12 provided by dipole antenna 51. The radio-frequency energy provided to each of the antennas is phased so that one lobe 81 of dipole pattern 12 is in time-phase with uniform pattern 11, and the opposite lobe 82 of dipole radiation pattern 12 is time-phased 180 degrees with uniform pattern 11. These instantaneous timepolarities are shown by plus and minus signs in Figure 1.

In-phase lobe 81 adds in a polar manner to uniform radiation pattern 11, and out-of-phase lobe 82 subtracts in a polar manner from pattern 11 to thus cause resultant radiation pattern 10. Since figure-eight pattern 12 rotates with the dipole antenna, the cardioid-type pattern likewise rotates with it at a speed which ordinarily is thirty cycles per second.

The dipole antenna is only a small fraction of a wavelength from the wall of the cylindrical antenna; and, for the most part, figure-eight radiation pattern 12 passes through the wall of slotted cylinder antenna 31 as if it were translucent. However, there is a certain amount of mutual-coupling between the conducting surface of the slotted cylinder antenna and the dipole antenna. This coupling induces currents in the slotted cylinder that flow in circular paths, such as those shown in Figure 10 as induced current circuits 86, 87, 88, and 89.

The four induced circuits diverge vertically toward a point P aligned with one end of dipole 51 and converge vertically away from a diametrically opposite point (not shown) aligned with the opposite end of the dipole. The vertical currents of the induced circuits combine to provide at one end of the dipole an upper vertical stream 91 and a lower vertical stream 92, which flow in opposing directions, and to provide at the other end of the dipole a similar set of opposing upper and lower vertical streams 93 and 94 (see Figure 3). The positions of the vertical streams are fixed relative to the dipole; and hence they rotate with the dipole.

The induced vertical currents are most dense at the unslotted upper and lower portions 37 and 38 of cylinder 31. This is due in part to the distribution of the horizontal currents in the induced circuits which is seen in Figure 10 by the arrowed horizontal portions of the induced currents. The horizontal current distribution is caused in part by the low impedance provided by the unslotted end portions of the cylinder compared to the high impedance provided by slotted portions. The result of this horizontal current distribution is that the vertical currents tend to concentrate at the unslotted upper and lower ends of the cylinder.

The vertical current streams 91, 92, 93,-and 94 cause vertically polarized radiation to be transmitted from the antenna system in the form of a figure-eight pattern in the horizontal plane which is shown as pattern 13 in Figure 1. Vertically polarized pattern 13 is spaced by ninety horizontal degrees from main figure-eight pattern 12 of horizontally polarized radiation. Accordingly, pattern 13 is space-phased by ninety degrees from pattern 12 as they rotate together.

The adverse effects of the vertically polarized energy are caused by the ninety degree space-phasing because it tends to provide directional information to a distant receiver, that might be on an airplane, which is ninety degrees different than the directional information provided by main figure-eight pattern 12 of horizontally polarized energy. The received directional information is therefore in error by an amount that depends on the amount of vertically polarized energy received. The invention suppresses this vertically polarized energy over a large vertical angle adjacent to the horizon where aircraft fly when distant from an omni-range beacon.

If the slotted antenna system were situated in space away from major reflection surfaces and without groundplane 23, the vertically polarized signals can be suppressed about the equatorial plane of the antenna (represented by line 96 in Figure 3) by making equal the axial dimensions A and B of cylindrical antenna 31. Then, equal cylinder wall portions are provided to induced current circuits 86, 87, 88 and 89; and hence, the upper and lower vertical current streams are equal. The diametrically positioned upper current streams provide radiation that is equal but oppositely phased from the radiation of the lower current streams; and there results a vertical radiation pattern which is shown in Figure 2. The instantaneously opposing polarities of the equal radiations cause complete cancellation along the equatorial plane 96 of the cylinder 31; and relatively little vertically polarized energy exists over a large vertical angle on either side of the equatorial plane.

Ordinarily, the antenna system cannot be located in outer space but must be mounted close to the earth. Thus, ground reflection of the lower radiation lobes occurs to change the radiation pattern of the antenna; and vertically polarized components are then reflected toward the horizon to cause substantial navigation errors for distant aircraft.

The invention provides the circular metallic groundplane 23 above true ground 21 to assist in suppressing the vertically polarized components transmitted toward the horizon. An extremely complex set of interactions result among the component radiations, true ground, and circular ground-plane 23; and among other things, suppression of the vertically polarized components is dependent upon the height of the antenna above both ground-planes, the diameter of the antenna, the radius of circular ground-plane 23, and the dimensions A and B.

The vertical current streams induced in the cylindrical antenna by the dipole antenna are not equidistant from ground plane 23, as is evident in Figure 3; but the upper vertical currents are more distant than the lower vertical currents. Line 97 in Figure 3 indicates the distance traveled by upper stream radiation to the edge of ground-plane 23, and line 98 indicates the distance traveled by lower stream radiation.

Because of the variation in distances 97 and 98, it is necessary to make dimension A slightly greater than dimension B'so'that the energy received at the edge of the ground-plane from the upper streams equals the energy received from the lower streams. Thus, the edge of the ground plane has a more equal effect upon the radiation from the upper and lower current streams when dimension A is slightly greater than dimension B.

The detailed theory involved in the invention for suppressing the vertically polarized radiation toward the horizon without effecting the horizontally polarized radiation is unknown at this time; and the mutual couplings and interactions involved are so complex that they defy mathematical analysis. One possible explanation for the system which has a ground-plane constructed in the above described manner is that the edge of the ground-plane provides more reflection to the lower vertical currents on the surface of the cylinder; and hence, they radiate more energy per unit of axial length than the upper vertical currents. Thus, dimension B is made less than dimension A to provide equal radiation from the upper and lower cylindrical portions.

A particular embodiment, which has been successfully operated as a model of the invention, obtains substantially complete suppression of vertically polarized components, which would be radiated toward the horizon due to ground reflections. This embodiment used twelve slots that were 0.393 wavelength long with their midpoints located five-eighths of a wavelength above ground-plane 23 which was provided with a radius of 0.785 of a wavelength, including one setting of rods 24. The diameter of cylinder 31 was 0.445 wavelength, and dimension A was made slightly greater than dimension B with dimension A equal to 0.216 wavelength and dimension B equal to 0.184 wavelength.

It is therefore noted that this invention provides an omni-directional antenna system which suppresses vertically polarized radiation in all horizontal directions over a relatively large vertical angle with respect to the antenna. Thus, an aircraft flying at a constant altitude along the contour of the earths surface will be within the suppression angle for vertically polarized radiation while the aircraft is distant from an omni-range beacon where positional error caused by the vertically polarized radiation would be significant. It is also apparent that this invention provides an omni-range antenna system which may have a diameter substantially less than onehalf wavelength of radiated energy, and furthermore the invention teaches how a slotted cylindrical antenna may be formed either in outer space or in proximity to a ground-plane to control the cancellation of certain vertically polarized radiation caused by the dipole antenna.

I have disclosed only a particular embodiment of my invention for clarity but it will be readily understood that the system may be modified in the manner taught by this specification. Thus, I desire it understood that no limitations upon my invention are intended except as may be inserted by the scope of the appended claims.

While I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. A slotted cylinder omni-directional antenna located in an upright manner above the center of a circular ground-plane for eliminating certain vertically polarized radiation caused by a dipole antenna contained centrally within said cylindrical antenna, the improvement comprising, upper and lower unperforated cylindrical portions formed at opposite ends of said cylinder, the axial dimension of said cylindrical portion nearest the ground plane being slightly smaller than the axial dimension of the opposite cylindrical portion, and said dipole located substantially midway between the adjacent ends of said portions, whereby vertically polarized radiation is suppressed about a horizontal plane through the slotted cylinder antenna.

2. Means for suppressing certain parasitic vertically polarized radiation from an antenna system situated adjacent a ground-plane comprising, a slotted cylinder antenna formed with a plurality of equally spaced longitudinal slots approximately one-half wavelength long at the radiated frequency, the slots located equidistant from said ground plane with their midpoint approximately fiveeighths of a wavelength at the radiated frequency above the ground plane, the cylinder antenna formed with portions above and below the slots, the cylinder portion farthest from the ground-plane having an axial dimension of approximately 0.216 wavelength at the radiated frequency, the lower cylindrical portion having an axial dimension of approximately 0.184 wavelength at the radiated frequency, and a dipole antenna supported transversely within the cylindrical antenna at the vertical midpoints of said slots, whereby the dipole causes parasitic vertically polarized radiation which is suppressed in the equatorial plane of the cylindrical antenna.

3. An omni-directional range navigation antenna system for location in free space wherein vertically polarized directional radiation is suppressed in a predetermined vertical direction comprising, a slotted cylinder omni-directional antenna, cover members supported across both ends of said cylindrical antenna, the portions of said cylindrical antenna above and below the slots formed with substantially equal axial dimensions, a dipole antenna supported rotatably within and midway between the vertical ends of said slots, driving means connected mechanically to said dipole for rotating it at a predetermined synchronous speed, radio-frequency oscillation means connected to said dipole to provide a directional radiation, a plurality of conductors equal in number to the slots supported insulatingly in said cylindrical antenna and converging together at one end of said cylinder antenna, each of said conductors following in an insulated manner the internal surface of said cover member and said cylindrical antenna between a different pair of slots until the vertical midpoints of the slots are approached, each conductor bending transversely in a single rotational direction across a respective slot and electrically connecting to the midpoint of the opposite side of its slot, an unbalanced source of radio-frequency oscillation connected on one side to the common connection of said conductors and connected on its other side to the adjacent cover member, and the phase of the radio-frequency oscillations received by the two antennas adjusted so that one horizontally polarized lobe of the dipole is in phase with the horizontally polarized uniform radiation of the slotted antenna and the opposite horizontally polarized lobe of the dipole is degrees out of phase with the uniform radiation.

4. An omni-directional range navigation antenna system for suppressing vertically polarized directional radiation in a predetermined plane parallel to an adjacent ground-plane, the system comprising, a slotted cylindrical antenna located above said ground-plane for providing a horizontally polarized signal substantially uniform in all horizontal directions, said cylinder having portions above and below the slots, the portion nearest the ground-plane having a slightly smaller axial dimension than the opposite portion, a dipole antenna rotatably supported within said cylindrical antenna for providing directional radiation, said dipole rotating in a plane transverse to the axis of said cylindrical antenna and the plane intersecting the midpoints of said slots, a plurality of conductors each connected at one end to the midpoint of one side of a dififerent slot, the portion of each conductor adjacent its slot connected end supported transversely over said slot in a like rotational direction, the remaining portions of said conductors supported insulatingly from the internal surface of the cylinder with their remaining ends connected together, unbalanced transmission means connected on its ungrounded side to the common connection of said conductors, a balanced transmission means connected to the dipole antenna, driving means for rotating said dipole antenna at a synchronous speed, radio-frequency energy means connected to the other ends of each of said transmission means to energize said antennas, phase-adjusting means connected serially with one of the transmission means to adjust the phase between the radio-frequency energy delivered to the two antennas to provide one lobe of horizontally polarized dipole radiation in phase with the slotted cylinder radiation, whereby a rotating directional signal is provided which has its vertically polarized components suppressed in the horizontal plane of said dipole.

5. A device as in claim 4 wherein the diameter of the cylindrical antenna is less than one-half wavelength of the radio frequency energy, and equal inductances are serially connected in a balanced manner with the input of the dipole antenna so that the resonant length of the dipole is substantially less than one-half a wavelength.

6. Means for providing horizontally polarized radiation with undesired vertically polarized component signals suppressed in a predetermined horizontal plane comprising, a circular ground-plane of metallic material supported horizontally and having a radius of approximately threequarter wavelength at the radiation frequency, a cylinder of metallic material having a diameter of approximately 0.445 wavelength supported in an upright manner above the center of the ground plane, the cylinder formed with a plurality of vertical slots approximately one-half wavelength long with their upper and lower ends lying in respective horizontal planes, the cylinder also formed with a portion above the slots having an axial length of approximately 0.216 wavelengths and a portion below the slots having an axial length of approximately 0.184 wavelength, cover members of metallic material supported across the upper and lower ends of said cylinder, a dipole antenna supported rotatably within said cylinder with its center intersected by the axis of the cylinder, said dipole being in a plane that intersects the vertical midpoints of said slots, the vertical midpoints being approximately fiveeighths of a wavelength above the ground-plane, and a 10 radio-frequency source connected to said dipole to provide a directional radiation pattern composed substantially of horizontally polarized components and very little vertically polarized components with the vertical components having a null axis in the horizontal plane of said dipole.

7. A device as in claim 6 wherein the ground-plane has a plurality of adjustable rods projecting radially from it, said rods spaced from each other by less than onequarter wavelength at the minimum radiated frequency, whereby the antenna system suppresses the vertically polarized components over a wide frequency range on either side of the designated frequency by radial adjustment of the rods.

8. A device as in claim 7 including, rotary condenser means coupling the signal to the dipoles, a pair of inductances connected serially with the respective legs of the dipole, whereby the length resonant of the dipole may be substantially less than one-half wavelength for resonance at the signal frequency.

9. A device as in claim 8 for providing an omni-directional signal with a directional signal, and including, a plurality of conductors connected together at one end and respectively connected at their other ends to one side of said slots, each of said conductors insulatingly passing over the vertical midpoints of their respective slot in one rotational direction, and a source of radio-frequency signal connected to the common connection of conductors, and the signal received by the slots adjusted in phase with the signal received by the dipole to provide one horizontally polarized dipole lobe in phase with the horizontally uniform radiation from the slotted antenna.

References Cited in the file of this patent UNITED STATES PATENTS 2,532,919 Johnson Dec. 6, 1950 2,622,199 Ramsay et al Dec. 16, 1 952 2,654,842 Engelmann Oct. 6. 1953 

